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Agriculture

Abstract

Grapevine species Vitis aestivalis and Vitis vinifera differentiate in their response to the powdery mildew fungus (PM). The High Performance Liquid Chromatography (HPLC) assays indicated that salicylic acid (SA) levels were higher in PM-resistant V. aestivalis 'Norton' than in PM-susceptible V. vinifera 'Cabernet sauvignon' under field conditions. It was also found that SA levels did not change in PM-infected Cabernet Sauvignon leaves at 24 hours post inoculation (hpi) and 48 hpi, but significantly increased at 120 hpi with PM. The results support the hypothesis that grapevine mounts defense responses against PM by enhancing SA levels, and natural disease resistance of a grapevine is likely associated with high levels of endogenous SA. We further compared transcript levels of key SA-associated genes in Norton and Cabernet Sauvignon leaves by quantitative reverse transcription-polymerase chain reactions (qRT-PCR). The genes EDS1, PAD4, EDS5, SAMT, SABP2, SAGT, NPR1, WRKY70 and ICS1 that are involved in SA-mediated defense pathways were selected. No significant difference was observed in the transcript levels of ICS1 and SAGT between Norton and Cabernet Sauvignon leaves. Transcript levels of EDS1, PAD4, SABP2, NPR1 and WRKY70 were significantly higher, while SAMT and EDS5 transcript levels were significantly lower, in Norton than in Cabernet Sauvignon leaves. Particularly EDS1 transcripts are 10 times more abundant in Norton that in Cabernet Sauvignon leaves. These results demonstrated that SA-associated signaling genes downstream of SA are transcribed at elevated levels in Norton leaves, which might result from the high endogenous SA levels of Norton.